In the field of automobiles, in terms of improvement of fuel efficiency, there is a growing need for a weight reduction of vehicle body, and in terms of securing collision safety, various high-strength steel sheets are applied to automobile members. However, even when yield strength and tensile strength of a steel product are improved by using a strengthening mechanism such as structure strengthening or a grain refining effect, a Young's modulus does not change. Therefore, when a sheet thickness of a steel sheet is thinned for weight reduction, member rigidity is decreased, so that it becomes difficult to achieve sheet thinning.
On the other hand, the Young's modulus of iron is 206 GPa or so generally, but it is, possible to increase a Young's modulus in a specific direction by controlling a crystal orientation (texture) of a polycrystalline iron. There have been made many inventions with regard to a steel sheet in which a Young's modulus in a direction perpendicular to a rolling direction (to be referred to as a transverse direction, hereinafter) is increased by increasing the integration degree to the {112}<110> orientation, for example, so far. However, the {112}<110> orientation is an orientation to significantly decrease r values in the rolling direction and in the transverse direction, so that there is a problem that deep drawability deteriorates significantly. Further, the Young's modulus in a rolling 45° direction decreases more than that of a normal steel sheet, so that the steel sheets can be applied only to a member long in one direction such as a frame member, and there is a problem that they cannot be applied to, for example, a panel member and a member required to have Young's modulus in plural directions such as torsional rigidity.
Patent Documents 1 to 4 are each related to an orientation group including {112}<110> or a steel sheet in which an orientation group including {112}<110> is developed. Patent Documents 1 to 4 are each related to a technique in which a high Young's modulus is obtained in a transverse direction and a certain direction of a member is suited to the transverse direction, thereby making it possible to increase rigidity in the direction. However, in each of Patent Documents 1 to 4, there is no description other than the Young's modulus in the transverse direction. Patent Document 3 among them is one related to a high-strength steel with ductility and a Young's modulus both achieved, but has no description on deep drawability. Further, Patent Document 4 is one related to a steel sheet excellent in hole expandability being one of indices of workability and in a Young's modulus, but has no description on deep drawability.
Further, some of the present inventors and the like have disclosed a hot-rolled steel sheet having a high Young's modulus in a rolling direction, a cold-rolled steel sheet, and manufacturing methods of the same (see Patent Documents 5 and 6, for example). These Patent Documents 5 and 6 are a technique of increasing Young's modulus in a rolling direction and in a rolling perpendicular direction by using the {110}<111> orientation and the {112}<111> orientation. However, with regard also to the steel sheets described in these respective Patent documents, there are descriptions on hole expandability and ductility, but there is no description on deep drawability.
Further, Patent Document 7 discloses a technique of increasing Young's modulus in a rolling direction and in a transverse direction of a cold-rolled steel sheet, but has no description on deep drawability.
Further, Patent Document 8 discloses a technique of increasing a Young's modulus and deep drawability by using an ultralow carbon steel. However, the technique described in Patent Document 8 has a problem that due to performing rolling with the total reduction amount of 85% or more in a temperature range of Ar3 to Ar3+150° C. or lower, and the like, a load on a rolling mill is high. Further, Patent Document 8 is not the one capable of obtaining significant rigidity at all because the Young's modulus in a 45° direction is not necessarily high and a crystal orientation to be developed is not also proper.